1. Field of the Invention
The present invention relates to photodiode sensor arrays used for a multiplicity of optical resolutions. In particular, the present invention regards photodiode sensor arrays for an optical encoder used for a multiplicity of resolutions.
2. Discussion of Related Art
Optical encoders for determining the relative position between two movable objects are well known. It is possible to determine relative positions in linear movement directions as well as in rotary movement directions. In these systems one object is usually connected with a scanning graduation while the other object is connected with a scanning unit. In the case of a linear encoder, a linear scale with a linear graduation is used whereas in the case of a rotary encoder a code disk with a circular graduation is used. The scanning unit used for either linear movement or rotary movement has one or more illumination sources and one or more optoelectronic detector elements. As detector elements e.g. photodiodes are usually used.
In the last several years, linear and rotary encoders have become more and more popular having a plurality of interdigitized photodiodes as detector elements. Sometimes such a detector arrangement is also called a phased array. Such an encoder and detector arrangement is shown in U.S. Pat. No. 6,175,109, the entire contents of which are incorporated herein by reference.
It is known that embodiments of the above-mentioned detector arrangements have photodiodes arranged in an array on a semiconductor chip. The arrangement of the photodiodes has to be tailored/designated for each encoder configuration in a unique way. This means that the required geometrical arrangement of the photodiodes, such as their width and spacing, depends on the scanning configuration, especially on the graduation period of the scanned scanning graduation. For a certain measurement resolution there exists a well-defined arrangement of photodiodes. Accordingly, if there is a need to change the scanning configuration or the resolution of the encoder, there will be a need to modify the design of the photodiode array in order to achieve the desired scanning configuration or resolution. An enormous amount of design work is necessary to modify the layout of the photodiode array in this case.
To solve the above problem, European Patent Specification EP 0 710 819 B1 suggests to use a single photodiode assembly with a plurality of photodiodes for several different scanning graduations having different graduation periods. For that purpose, only a certain number of all available photodiodes has to be activated in dependence of the scanning graduation. An adaptation procedure is necessary to determine in each case which of the photodiodes have to be activated for a certain scanning graduation. One important drawback of this system is that it requires a complex ASIC to control the adaptation procedure. Another disadvantage is that the system""s activation phase would require special tooling discs should light be allowed to shine on multiple incremental data signal groups. Furthermore, a lot of space of memories and associated circuitry on the carrier substrate is necessary which is contrary to a possible miniaturization of the system.
Another disadvantage of the system disclosed in EP 0 710 819 is the system""s index sensors for determining the absolute position. In particular, a disc with a pattern of openings that match the pattern of the index sensor allows light to move across the index sensors. The light completely illuminates the index sensors at only one point per rotation. During those times when the index sensors are partially illuminated, the signal is significantly smaller than when all of the index sensors are simultaneously illuminated.
Accordingly, it is an object of the present invention to easily modify the resolution of a detector array while allowing the detector array to have a desirable miniature size.
Another object of the present invention is to modify the resolution of a detector array without using an adaptation phase.
Another object of the present invention is to improve the strength of the absolute and relative position signals generated by a detector array at multiple resolutions.
One aspect of the present invention regards an optical encoder for providing position information of an object, which moves along a certain measuring direction, the encoder includes a light source that emits light and a data track attached to an object that moves relative to the light source, the data track receiving the light and comprising a plurality of alternating areas of different optical properties of a particular resolution. A detection system receives modulated light from the data track and generates a position signal from the received light. The detection system includes a photodiode array that receives the modulated light from the data track and a resolution selection unit connected to the photodiode array and which controls a resolution of the photodiode array, wherein all photodiodes associated with the photodiode array are active irrespective of a resolution selected by the resolution selection unit.
A second aspect of the present invention regards a method of controlling the resolution of an optical encoder for providing position information of an object, which moves along a certain measuring direction where the optical encoder includes a light source that emits light and a data track that moves relative to the light source. The method includes directing modulated light from the data track to a plurality of photodiodes of a detection system having a resolution that has a first value and changing the resolution of the detection system to a second value without altering an arrangement of the plurality of photodiodes of the detection system during the changing from the first value to the second value.
A third aspect of the present invention regards an optical encoder for providing position information of an object, which moves along a certain measuring direction. The encoder includes a light source that emits light, a data track attached to an object that moves relative to the light source, the data track receiving the light and having a plurality of alternating areas of different optical properties of a particular resolution. A detection system receives light from the data track and generates an index signal from the received light. The detection system includes an index photodiode array that receives the light from the data track and generates an index signal and a resolution selection unit connected to the index photodiode array and which controls contrast of the index signal.
A fourth aspect of the present invention regards a method of controlling an index signal of an optical encoder for providing position information of an object which moves along a certain measuring direction, where the optical encoder includes a light source that emits light and a data track that moves relative to the light source and has a given resolution. The method includes directing light from the data track to a plurality of photodiodes of an index photodiode array and changing the activation status of one or more of the photodiodes of the index photodiode array without altering an arrangement of the photodiodes of the index photodiode array so as to form an index signal.
Each aspect of the present invention provides the advantage of easily modifying the resolution of a detector array while allowing the detector array to have a desirable miniature size.
Each aspect of the present invention provides the advantage of not requiring an adaptation phase to determine the photodiodes to be activated in an array for a particular resolution. Elimination of the need of an activation phase provides the additional advantage that special tooling discs are not required such as would be needed for the system described in EP 0 710 819 should light be allowed to shine on multiple incremental data signal groups.
These and other features and advantages of the present invention will be appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings.